A wave reduction gear is composed of an annular rigid internal gear, a flexible external gear disposed therein, and a wave generator which flexes the flexible external gear in the radial direction to mesh with the rigid internal gear and causes to move the meshing position of the gears in the circumferential direction. In an actuator composed of a motor and this wave reduction gear, the rotating shaft of the motor is coaxially connected to the wave generator, and considerably reduced rotations are outputted from the rigid internal gear or the flexible external gear in accordance with the difference in the number of teeth between the two gears.
With an actuator thusly configured, the wave reduction gear is coaxially disposed at the distal end of the motor, and a magnetic position detector is mounted on the rear end portion of the rotating shaft of the motor projecting from the rear end of the motor, as disclosed in Patent Document 1 noted below. However, the configuration in which the wave reduction gear, motor, and position detector are coaxially arranged along the axial direction of the actuator is unsuitable for making the actuator flatter.
In contrast, in the actuator disclosed in Patent Document 2, a configuration is proposed in which a magnetic encoder is mounted in a location on the rotating shaft of a motor positioned inside the wave reduction gear. The interior space of the wave reduction gear can be used as space for disposing a magnetic encoder, whereby the entire length of an actuator can be reduced by an amount commensurate with the axial length of the magnetic encoder.
[Patent Document 1] JP-A No. 2006-149139
[Patent Document 2] JP-A No. 2005-312223
Here, a circuit board on which a sensor signal converter is mounted for processing the detection signals of an angle detector (magnetic sensor) of the magnetic encoder is generally disposed on the rear end side of the motor. When the angle detector of the magnetic encoder is incorporated inside wave reduction gear, the angle detector and the circuit board must be connected by wiring.